1. Field of the Invention
The present invention pertains to a method of manufacturing acrylic acid esters and methacrylic acid esters by catalytic addition of the corresponding acid to an alkene. The invention particularly pertains to a method of manufacturing isobornyl acrylate and isobornyl methacrylate.
2. Description of the Related Art
Carboxylic acids can be added to olefins under acid catalysis, to equilibrium conversion. This method represents a supplement to the customary transesterification or esterification reactions; with olefin addition one can produce esters of secondary and particularly tertiary alcohols, which otherwise are difficult to produce. Catalysts used may be proton acids or Lewis acids such as boron trifluoride (see Houben-Weyl, 1952, Vol. 8, p. 534). The higher the degree of substitution (by alkyl substituents) at the double bond and the more acidic the carboxylic acid, the more favorable is the equilibrium to the side of the ester.
Examples which might be cited are the production of acetates or formates from isobutene, isopentene, dicylopentadiene, norbornene, or camphene. The production of isobornyl acrylate from camphene and acrylic acid, with H.sub.2 SO.sub.4 as catalyst, is described in Japanese Pat. 79-126293 (ref.: CA 92:60,517).
Acid ion exchangers have also been used as catalysts for the reaction. Thus, the production of isobornyl (meth)acrylate from camphene and (meth)acrylic acid using a strongly acid ion exchanger is described in Japanese Pat. 58-049337. However, in this process, long reaction times (&gt;8 hr) are needed to reach equilibrium conversion. This results in poor space-time yields, with a detrimental effect on manufacturing costs. Also, operating over such long reaction times at high temperatures necessitates stabilization of the reaction mixture (to avoid polymerization), and may additionally present more serious problems.
German laid-open application DE 19 54 986 claims heteropolyacids of molybdenum or tungsten as catalysts to produce organic compounds by reacting olefins with carboxylic acids (including unsaturated carboxylic acids) to form the corresponding esters. According to German laid-open application DE 30 34 033, dihydrodicyclopentyl acrylate (or methacrylate) can be produced by reacting dicyclopentadiene, an endocyclic diolefin, with acrylic acid or methacrylic acid respectively, in the presence of a tungsten heteropolyacid compound as catalyst. The present applicants were unable to successfully employ tungsten heteropolyacid catalysis in the reaction of camphene with (meth)acrylic acid, however.
Industry has been deterred in the greater use of the interesting compounds isobornyl acrylate and isobornyl methacrylate, particularly as comonomers in the production of industrially and commercially useful polymers, due to insufficiencies in the known manufacturing methods for the subject compounds.
Industrial use of the known methods is difficult due to factors such as long reaction times as in the above-mentioned acid ion exchange catalysis; corrosion effects of mineral acids and boron trifluoride on process equipment; and the need to neutralize such soluble catalysts and remove them from the product by water washing and/or extraction of the reaction mixture, all of which make the refining of the product quite complex. Moreover, catalysts such as many Lewis acids present problems with respect to environmentally acceptable disposal. Purification by distillation of the product in the presence of the catalyst is not possible because unreacted carboxylic acid (which is volatile) will be distilled off, which will shift the reaction equilibrium away from formation of the ester.